This invention relates to syringes, and more particularly to improvements in safety syringes of the kind in which a needle assembly can be withdrawn into a safe location within the barrel of the syringe after use.
Safety syringes in which the needle can be withdrawn into the barrel are described in numerous U.S. patents, including the following U.S. patents:
U.S. Pat. No. 4,927,414 May 22, 1990
U.S. Pat. No. 4,950,241 Aug. 21, 1990
U.S. Pat. No. 4,995,870 Feb. 26, 1991
U.S. Pat. No. 5,125,899 Jun. 30, 1992
U.S. Pat. No. 5,290,233 Mar. 1, 1994
U.S. Pat. No. 5,328,475 Jul. 12, 1994
U.S. Pat. No. 5,338,304 Aug. 16, 1994
U.S. Pat. No. 5,431,631 Jul. 11, 1995
U.S. Pat. No. 5,431,632 Jul. 11, 1995
U.S. Pat. No. 5,533,975 Jul. 9, 1996
U.S. Pat. No. 5,569,203 Oct. 29, 1996
U.S. Pat. No. 5,575,774 Nov. 19, 1996
U.S. Pat. No. 5,578,015 Nov. 26, 1996
U.S. Pat. No. 5,772,687 Jun. 30, 1998
U.S. Pat. No. 5,968,020 Oct. 19, 1999
U.S. Pat. No. 5,993,419 Nov. 30, 1999
U.S. Pat. No. 6,033,385 Mar. 7, 2000
Known syringes having a needle withdrawal feature have a number of disadvantages that have inhibited them from wide acceptance.
In most of the known syringes of this type, accidental premature interlocking of the plunger with the needle assembly can occur when the plunger is moved forward. In others, complicated measures are necessary to avoid premature interlocking.
Another problem is that the releasable connection between the needle base and the syringe barrel can be too weak, so that the needle assembly can be pushed into the barrel in the process of inserting the needle through the stopper of a vial or through the skin of a patient. Alternatively, the connection between the needle base and the syringe barrel can be stronger than the connection made between the plunger and the needle assembly, in which case the latter connection can be broken as the plunger is withdrawn in an attempt to pull the needle assembly into the barrel. Still another problem is that, even after the needle is withdrawn into the syringe barrel, it is possible for the needle to be returned to its projecting condition, either by movement of the plunger in the distal direction, or in other ways, such as by tampering, if the plunger is broken off.
Known safety syringes are also subject to various Other disadvantages, including complexity of construction, high manufacturing costs, inadequate strength, lack of versatility, and other deficiencies in safety and reliability. Moreover, most known safety syringes require the manipulations in addition to, or different from, the manipulations carried out in the use of a conventional non-safety syringe.
Among the objects of this invention, therefore, are the avoidance of some or all of the aforementioned problems, and the achievement of a safe, simple, inexpensive, reliable, versatile, and otherwise generally acceptable safety syringe.
The safety syringe according to the invention comprises an elongated barrel having proximal and distal ends, a cylindrical interior wall, and openings at the proximal and distal ends. A standard needle assembly, comprising a hollow needle and a needle base, is provided on the barrel, the needle base being removably held in the distal end opening of the barrel with the needle projecting therefrom externally of the barrel in the direction of barrel elongation. A plunger extends through the proximal end opening of the barrel and has a resilient plunger tip sealingly engaged with the cylindrical interior wall of the barrel and slidable along said wall to draw fluid into the barrel through the needle and to expel fluid from the interior of the barrel through the needle. Interlockable elements on the needle base and plunger are provided for connecting the needle base to the plunger when the plunger tip is moved in the distal direction past a predetermined position, so that the needle base and plunger may be connected with each other, and the needle assembly can be drawn into the interior of the barrel by movement of the plunger in the proximal direction.
A latch connects the plunger with the barrel when the plunger tip is adjacent the distal end of the barrel but not past said predetermined position in the distal direction. The latch preferably comprises a tab hinged by a live hinge to a finger flange of the barrel, and engageable with a notch formed in the plunger at a position such that, when the latch is engaged with the notch, it prevents distal movement of the plunger to a position at which the interlockable elements of the needle base and the plunger become engaged. The latch, however, is readily released by proximal movement of the plunger. Thus, upon proximal movement of the plunger to draw fluid into the barrel through the needle, and distal movement of the plunger to expel fluid from the barrel through the needle, the interlockable elements of the needle base and plunger may be operated to connect the plunger to the needle base for withdrawal of the needle assembly into the barrel. The latch reliably prevents accidental premature interlocking of the plunger with the needle assembly, yet is easily disabled as the plunger is pulled back to draw fluid into the syringe barrel through the needle.
A projection is provided on the plunger adjacent the plunger tip, and a resilient insert is secured to the barrel adjacent the proximal end of the barrel. The plunger extends through the resilient insert, and the resilient insert permits movement of the plunger in the direction of elongation of the barrel. The resilient insert has a cam surface engageable by the projection on the plunger to expand the insert when the plunger is withdrawn past a predetermined position in the proximal direction. The cam surface, however, permits resilient contraction of the insert when the plunger moves farther in the proximal direction. The plunger and insert have latching surfaces which move past each other when the insert is expanded by the engagement of the cam surface by the projection. The latching surfaces are engageable with each other when the insert resiliently contracts after the plunger makes said movement farther in the proximal direction, to prevent distal movement of the plunger after the needle assembly is withdrawn into the interior of the barrel. The resilient insert reliably prevents distal movement of the plunger after the needle assembly is withdrawn into the interior of the barrel.
In a preferred embodiment of the invention, the resilient plunger tip is hollow, and the interlockable elements include a barbed, sharp-tipped, projection projecting in the proximal direction from the needle base and a pair of opposed, resilient jaws formed on the plunger and located within the hollow plunger tip. The sharp=tipped projection is capable of penetrating the membrane which forms the face of the hollow plunger tip, and the resilient jaws have hook-shaped tips, spaced from each other by a distance less than the width of the barbed, sharp-tipped projection. The jaws are movable apart from each other by the projection, and engageable with the barbs of the projection to connect the needle base to the plunger. These interlocking elements securely connect the needle base to the plunger and ensure that the needle assembly will be reliably withdrawn into the barrel.